Fatty acids are one of the principal components of lipids. In vivo, fatty acids are bonded to glycerin via an ester bond to form lipids such as triacylglycerol. Further, many animals and plants also store and utilize fatty acids as an energy source. These fatty acids and lipids (fats and oils) stored in animals and plants are widely utilized for food or industrial use.
For example, higher alcohol derivatives that are obtained by reducing higher fatty acids having approximately 12 to 18 carbon atoms are used as surfactants. Alkyl sulfuric acid ester salts, alkylbenzenesulfonic acid salts and the like are utilized as anionic surfactants. Further, polyoxyalkylene alkyl ethers, alkyl polyglycosides and the like are utilized as nonionic surfactants. These surfactants are used for detergents or disinfectants. Cationic surfactants such as alkylamine salts and mono- or dialkyl-quaternary ammonium salts, as other higher alcohol derivatives, are commonly used for fiber treatment agents, hair conditioning agents or disinfectants. Further, benzalkonium type quaternary ammonium salts are commonly used for disinfectants or antiseptics. Furthermore, vegetable fats and oils are used also as raw materials of biodiesel fuels.
A fatty acid synthesis pathway of plants is localized in a chloroplast. In the chloroplast, an elongation reaction of the carbon chain is repeated starting from an acetyl-ACP (acyl-carrier-protein), and finally an acyl-ACP (a composite consisting of an acyl group being a fatty acid residue and an acyl-carrier-protein) having 16 or 18 carbon atoms is synthesized. A β-ketoacyl-ACP synthase (β-ketoacyl-acyl-carrier-protein synthase: hereinafter, also referred to as “KAS”) is an enzyme involved in control of chain length of the acyl group, among enzymes involved in the fatty acid synthesis pathway. In the plants, four kinds of KASs having different function respectively, namely KAS I, KAS II, KAS III and KAS IV are known to exist. Among these, KAS III functions in a stage of starting a chain length elongation reaction to elongate the acetyl-ACP having 2 carbon atoms to the acyl-ACP having 4 carbon atoms. In the subsequent elongation reaction, KAS I, KAS II and KAS IV are involved. KAS I is mainly involved in the elongation reaction to the palmitoyl-ACP having 16 carbon atoms, and KAS II is mainly involved in the elongation reaction to the stearoyl ACP having 18 carbon atoms. On the other hand, it is believed that KAS IV is involved in the elongation reaction to medium chain acyl-ACP having 6 to 14 carbon atoms. Less knowledge for the KAS IV is obtained even in the plants, the KAS IV is considered to be KAS characteristic to the plants accumulating a medium chain fatty acid, such as Cuphea (see Patent Literature 1 and Non-Patent Literature 1).
Cyanobacteria (blue-green bacteria) belong to a group of eubacteria, and have an ability to produce oxygen through photosynthesis and fix carbon dioxide. Cyanobacteria, which have an outer membrane and a cell wall formed of peptidoglycan, and fall into the category of gram-negative bacteria. However, cyanobacteria are phylogenetically far from typical gram-negative bacteria in the taxonomy. More than billion years ago, cyanobacteria were engulfed by eukaryotic cells. Such intracellular symbiont (primary symbiosis), cyanobacteria, are considered as an origin of chloroplasts. Thus cyanobacteria have been widely used in photosynthesis studies as an ancestor organism of chloroplasts. Further, cyanobacteria grow faster than other plants, and have high photosynthetic ability. Furthermore, cyanobacteria also have a transformation ability.
Because of this, cyanobacteria, to which foreign DNA is introduced in the cells, can be used in microbiological production of substances, and thus have attracted attention as a host for producing substances such as biofuel.
As examples of producing substances using cyanobacteria, production of fatty acids has been reported (Non-Patent Literature 2). However, with regard to a technology on the production of fatty acids, depending on the photosynthesis of cyanobacteria and using carbon dioxide in the atmosphere or the like as a carbon source, productivity thereof has still remained at a low level.